One of our three native snakes, the adder is the UK’s only venomous snake.  However, they are not aggressive and no one has died from an adder bite in the UK for at least 20 years.


IUCN Red List Status:  Least concern.

Distribution:  Found in woodland, heathland and moorland across UK, except Channel Islands, Scilly Islands, Northern Ireland, Scottish islands and Isle of Man.  Widespread across Europe from Scandinavia and the Baltic to UK and France, then eastwards to Russia, Mongolia, Democratic People's Republic of Korea and northwestern China.

Habitat:  Rough open countryside such as heathland and moorland and the edges of woodlands, where plenty of sunlight hits the ground.

Life-span:  15-20 years.

Size:  Males up to 60cm, females up to 80cm long.  Weight: 50-60g (males) and 80-100g (females).

Description:  Small snake with distinctive dark zig-zag pattern down its back.  Females are light to reddish brown, while males are greyish in colour.  Occasionally, adders are melanistic (entirely black). Eyes are red.

Food:  Small mammals, lizards and ground-nesting birds like meadow pipits and skylarks.  

Adder habits

Adders are the most commonly seen snakes in the UK, mostly because they are less likely to move into cover if disturbed.  They hibernate through the winter and emerge in early spring. Males shed their winter skin and are ready for mating by the middle of April.  Females incubate their eggs internally, giving birth to up to 20 live young in August or September.

Like other reptiles, adders are ectothermic, meaning that they cannot generate their own body heat.  As a result, they need to raise their body temperature to 25℃ to 30℃ before they can become fully active and will bask in patches of sunlight to raise their temperature.  Pregnant females bask in the sun to aid the development of their young inside their bodies. In the UK, it is often May before daytime temperatures are high enough for adders to being hunting for food.

When hunting, adders strike swiftly, delivering a venom-injecting bite to their prey.   Then they wait for the prey to die before swallowing it whole. They are able to extend their jaws to swallow prey much bigger than their heads, whilst their ribs are not joined and can also open outwards to accommodate much larger prey.  Their digestive juices are very powerful, so only the teeth and hair of a rodent pass through the snake.

Adders and humans

Adders are secretive and non-aggressive.  They never set out looking for humans to bite, so if you leave them alone, they will do the same for you.  They have a highly developed venom injecting mechanism, but will only bite as a last resort. You are very unlikely to be bitten unless you either tread on an adder by mistake or attempt to handle them.  Even if bitten, with proper treatment, the worst effects tend to be bruising and nausea, with just ten human deaths from adder bites recorded in the UK in the last 100 years.  That said, adder bites are very painful!

Threats to the adder

Young adders and even occasionally adult snakes are vulnerable to being eaten by birds like crows and buzzards.  They can also be eaten whilst in hibernation by rodents.

Protecting the adder

Adders are protected by law in the UK against being killed,  injured or traded by humans.


All photos by Iain Leach, courtesy of Wildscreen Exchange.

Factsheet created 31/07/2018. PL.

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